The present invention relates to a magnetic recording/reproducing apparatus and a magnetic recording medium.
Recently, a viewing screen is being increasingly widened with propagation of a so-called high-vision system having an aspect ratio of 16:9 and various modes of video signals are taken so as to maintain the interchangeability with the existing 4:3 aspect ratio system. For example, as the signal modes there are known a squeeze mode signal (full mode, shrink mode signal) in which a video signal having the aspect ratio of 16:9 is assigned to all the effective screen lines of a video signal having the aspect ratio of 4:3, a first letter box signal in which the upper and lower portions of a 4:3 aspect ratio screen are blackened in the state that the aspect ratio of 16:9 is maintained, and a second letter box signal in which picture additive information such as vertical resolution correction information is superimposed on the upper and lower portions of the 4:3 aspect ratio screen.
FIGS. 4A to 4C illustrate the states that the aforementioned signals are displayed on the 4:3 aspect ratio screen. FIG. 4(A) shows a screen of a video signal having the existing 4:3 aspect ratio for comparison purposes, FIG. 4(B) shows a screen of the squeeze mode signal where a circle positioned at the center portion of the screen takes a vertical ellipse configuration due to the assignment to all the effective screen lines of the 4:3 aspect ratio screen, and FIG. 4(C) shows a screen of the first or second letter box signal where, unlike the squeeze mode signal, the circle positioned at the center portion of the screen takes a true circle configuration and the upper and lower portions of the screen are blackened so as to maintain the 16:9 aspect ratio. In the case of the second letter box signal, the picture additive information is superimposed on the period corresponding to the black portions.
For coping with the various signal modes, it is desirable that the signal modes are discriminated by a VTR to obtain the discrimination information which is in turn recorded on a control track of a magnetic tape by varying the duty ratio of a control signal to be transmitted to a video apparatus such as a television receiver. In VHS-system home-use VTRs, as means to record information other than servo information by varying the duty ratio of the control signal, there is known a VISS.multidot.VASS (Video Index Search System.multidot.Video Address Search System) system which records the heading information of a program and others. In addition, a 4-head 270.degree.-winding camera-integrated VTR varies the duty ratio of the control signal to prevent the so-called back track reproduction under the state of maintaining the interchangeability with the aforementioned VISS.multidot.VASS system.
FIGS. 5A, 5B and 5C are illustrations for describing the control signal to be used in the VISS.multidot.VASS system. FIG. 5A shows a control signal not having the general VISS.multidot.VASS information where one period thereof takes the time period corresponding to one frame of a video signal, for example, in the NTSC system, the time period is 1/30 sec and in the PAL system the time period is 1/25 sec. The duty ratio of such a control signal is 50%, while the information necessary as the servo information is only the timing of the rising edge aa. Accordingly, in the VISS.multidot.VASS system, the falling edge which is unnecessary as the servo information, is used so that the information is recorded by varying the duty ratio of the control signal. That is, the control signal having a duty ratio of 60% shown in FIG. 5B indicates "0" and the control signal having a duty ratio of 27.5% illustrated in FIG. 5C indicates "1". The heading information of a program, address information and others are recorded by a combination of these numerals.
Secondly, a description will be made with reference to FIGS. 6A to 6F in terms of the prevention of the back track reproduction in the 4-head 270.degree.-winding camera-integrated VTR. In this camera-integrated VTR, a tape pattern illustrated in FIG. 6B is formed by first to fourth magnetic heads H1 to H4 provided on a rotary drum as illustrated in FIG. 6A. In FIG. 6B, first to fourth tracks T1 to T4 respectively correspond to the first to fourth magnetic heads H1 to H4. The recording is effected sequentially with respect to four tracks. Here, the first and second tracks T1 and T2 are referred to as first frame tracks and the third and fourth tracks T3 and T4 are referred to as second frame tracks. However, the control signal is recorded at every single frame, i.e., at every two tracks, and hence there is the possibility of an occurrence of the back track reproduction in which the first frame tracks are reproduced by the third and fourth magnetic heads H3 and H4 and the second frame tracks are reproduced by the first and second magnetic heads H1 and H2. In this case, the reproduction is effected by the magnetic heads different from the magnetic heads used for the recording. This results in the fact that difficulty is encountered to follow the curves of the track patterns inherent to the respective magnetic heads, thus deteriorating the S/N ratio of the reproduced signal. Accordingly, the information indicative of the magnetic head used for recording a specific track from among successive four tracks is recorded in correspondence with the first and second frame tracks by varying the duty ratio of the control signal and then detected at the time of the reproduction so as to control the phase of the magnetic head, which is refered to as 4-track sequence recording and reproducing. Here, for maintaining the interchangeability with the VISS.multidot.VASS system, it is required that the varied duty ratio of the control signal is distinguishable from the duty ratio of the VISS.multidot.VASS system. Thus, for the prevention of the back track reproduction, the control signals respectively having duty ratios of 62.5% and 30% as illustrated in FIGS. 6C and 6D are taken as "L" and the control signals respectively having duty ratios of 57.5% and 25% as illustrated in FIGS. 6E and 6F are taken as "S", and the repetitions of these "L" and "S" are recorded so as to be distinguishable from "0" and "1" in the VISS.multidot.VASS system. That is, the control signal having the duty ratio of 62.5% indicates "0" and "L", the control signal having the duty ratio of 30% indicates "1" and "L", the control signal having the duty ratio of 57.5% indicates "0" and "S", and the control signal having the duty ratio of 25% indicates "1" and "S". "L" and "S" are recorded in correspondence with the first and second frame tracks whereby it is possible to record the 4-track sequence necessary for the prevention of the back track reproduction. With the above-described arrangement, the conventional apparatus realizes the back track reproduction prevention by varying the duty ratio of the control signal in the state of maintaining the interchangeability with the VISS.multidot.VASS system.
There is a problem which arises with such a conventional technique, however, in that difficulty is encountered to record the back track reproduction prevention information concurrently with recording the discrimination information due to the discrimination of the signal mode by varying the duty ratio of the control signal and maintaining the interchangeability with the VISS.multidot.VASS system. In addition, it is also difficult to offer a recording medium for recording the discrimination information corresponding to the signal mode.